Latest weather model runs indicate the possibility for severe weather to affect southern Ontario early this weekend. It's still four days out, but it looks as though several ingredients may come into play to produce some significant weather somewhere in the province ahead of a cold front.

Models are in some agreement for this potential, IE several of them indicate pretty much the same thing, so it's looking at least hopeful. Timing of it all is the biggest factor. Right now, models align in almost perfect set up for the region, but things could rapidly change at a moments notice.

There is indications of a prime theta-e ridge pushing through southern Ontario Friday. Also, an ejection of ripe moist air into the southern Ontario region is also being indicated.

Will not speculate right now on conditions that could be expected. The day three tomorrow should give a good picture at what is possible. Any number of factors could ruin this potential, such as severe weather in the Midwest/NRN Plains developing in the wrong region, or moving to quickly or slowly, or busting, or cloud cover.

One thing to note: models indicated severe weather potential for today around SW ON/SW MI for the last few days. Last night, models dropped the risk. Even the Ohio Valley which looked primed for severe weather was dropped out of the risk by models barely without a moments notice.

__________________Regional Municipality of Waterloo, Ontario
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Note:
Probabilities are not based on wiether or not supercells or a derecho will occur. aka 30% probability of derecho composite at 3 doesn't mean 30% chance a derecho will happen.
The 'composite parameters' are based on the mean(average) calculations off atmospheric conditions where these types of storms have initiated. Higher values (between 1-6 (or higher)) tell us that the calculations put in (aka: cape, windshear, etc) are higher and more suitable for that type of storm. Having lower composite numbers for a derecho and vice versa does not mean it is less likely for another type of severe weather occurance.

__________________Love is like a flower, even the most beautiful kind dies.

EDIT Interesting to note, the latest SREF shows sigtor/mean pmsl parameters with the possible morning MCC from the Midwest, then as the MCC advances into NY, sigtor/mean PMSL parameters briefly redevelop back into southern Ontario behind it, then dissipate by 8pm.

__________________Regional Municipality of Waterloo, Ontario
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AS HAS BEEN COMMON FOR THE LAST SEVERAL DAYS...LOW LEVEL WARM
ADVECTION SHOULD AID A ZONE OF CONVECTION ALONG NOSE OF THE LLJ FROM
ERN NEB...ENEWD INTO THE LOWER GREAT LAKES. ALTHOUGH THERE WILL
LIKELY BE SOME DIURNAL COMPONENT TO THIS ACTIVITY...EPISODIC THUNDER
EVENTS WILL BE NOTED THROUGH THE PERIOD. ADDITIONAL CONVECTION
SHOULD DEVELOP ALONG THE COLD FRONTAL SURGE DURING THE LATTER HALF
OF THE PERIOD...LIKELY REINFORCING A LONGER-LIVED PRECIP EVENT INVOF
IA. DAMAGING WINDS SHOULD BE THE PRIMARY SEVERE THREAT WITH ANY N-S
BOW-TYPE STRUCTURES.

__________________Regional Municipality of Waterloo, Ontario
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3. FRIDAY..A POST-MCS BOUNDARY WILL LIKELY BE SET UP ACROSS
SOUTHWESTERN ONTARIO, AND STRONG SUSTAINED WEST-SOUTHWEST LOW LEVEL
JET ACROSS SOUTHERN ONTARIO WILL SUPPORT CONSIDERABLE AIRMASS
RECOVERY FRIDAY AFTERNOON. THE SREF INDICATES AMPLE MLCAPES OF 1500
TO 2500 J/KG FROM THE SOUTHWEST TOWARDS THE GOLDEN HORSESHOE. THE
GEM REGIONAL MAINTAINS EVEN MORE ROBUST MLCAPES OF 3000 ACCOMPANIED
BY SHEARS IN THE 0-3 KM LAYER OF 30 TO 40 KTS. BELIEVE A SECONDARY
RISK FOR SEVERE STORMS EXISTS FRIDAY AFTERNOON (POST-RECOVERY) WITH
LINE SEGMENTS AND SOME SUPERCELLS ACCOMPANIED BY THE WHOLE SUITE OF
RISKS FROM LARGE HAIL OF 3 CM, STRONG DAMAGING WIND GUSTS,
TORRENTIAL RAINFALL TO AN ISOLATED RISK OF A TORNADO. THE MAIN AREA
IS SOUTHWESTERN ONTARIO TO NIAGARA.

__________________Regional Municipality of Waterloo, Ontario
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The textbook supercell over Essex Couny has been rotating for 20 minutes now. All indications as far as I can tell are that this storm is producing or has produced a tornado somewhere between Amherstburg and Harrow.

EDIT: Intense rotation continues, now passing Harrow heading for Kingsville and Leamington. Radar presentation of this hook is extremely impressive.

The storm behind this one is tornado warned for Detroit.

EDIT: AFTER ALMOST THIRTY MINUTES OF INTENSE ROTATION AND HIGH INDICATION OF A TORNADO... ENVIRONMENT CANADA ISSUES A TORNADO WARNING RIGHT BEFORE THE STORM PASSES OVER LAKE ERIE.

__________________Regional Municipality of Waterloo, Ontario
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Guys i think we should give EC a big round of aplause for this wonderful job with the warnings today. Thanks for making people clueless and have a chance of being killed. Lets hope there are no injuris or fatalities. P.S i was joking about the aplause thing